The invention relates to a data carrier which is constructed for contactless communication with a station which is at least suitable for reading, and includes receiving means for receiving data blocks and transmission means for transmitting data blocks, and includes a circuit with a receiving terminal for receiving data blocks received by means of the receiving means and with a transmission terminal for outputting data blocks to be transmitted by means of the transmission means, and with time slot determination means which are arranged so as to determine each time slot of possibly repeatedly, successively running time slot sequences, each of which consists of a given number N of successive time slots, and with first processing means which are arranged to process a selection data block which is transmitted by a station in order to initiate a selection operation and is received via the receiving terminal and serves to select the data carrier from a plurality of data carriers, and with second processing means which are arranged to process, after the processing of a received selection data block by means of the first processing means, an identification data block which is stored in the circuit of the data carrier and can be applied, after its processing by means of the second processing means, during the duration of an nth time slot of a time slot sequence and via the transmission terminal, to the transmission means for transmission to a station, where 1xe2x89xa6nxe2x89xa6N, and with third processing means which are arranged to process, after correct reception in a station of an identification data block transmitted by the data carrier to this station, an acknowledge data block which is transmitted by this station to the data carrier and is received via the receiving terminal and is capable of setting the circuit of the data carrier to a selected state.
The invention also relates to a circuit which includes the following means, namely a receiving terminal for receiving received data blocks, and a transmission terminal for outputting data blocks to be transmitted, and time slot determination means which are arranged so as to determine each time slot of possibly repeatedly successively running time slot sequences, each of which consists of a given number N of successive time slots, and first processing means which are arranged to process a selection data block which is transmitted by a station, being at least suitable for reading, in order to initiate a selection operation and is received via the receiving terminal and serves to select the circuit from a plurality of circuits, and second processing means which are arranged to process, after the processing of a received selection data block by means of the first processing means, an identification data block which is stored in the circuit and can be applied, after its processing by means of the second processing means and during the duration of an nth time slot of a time slot sequence, to the transmission terminal for transmission to a station, where 1xe2x89xa6nxe2x89xa6N, and third processing means which are arranged to process, after correct reception in a station of an identification data block transmitted by the circuit to this station, an acknowledge data block which is transmitted by this station to the circuit and is received via the receiving terminal and is capable of setting the circuit to a selected state.
A data carrier of the kind set forth in the first paragraph and a circuit for a data carrier of the kind set forth in the second paragraph are known, for example from the patent document U.S. Pat. No. 5,539,394 A. When a known data carrier of this kind is present, together with a plurality of similar data carriers, within the communication range of a station which is at least suitable for reading, a data carrier can be selected in each time slot during a selection operation where a time slot sequence is executed. During such a selection operation, each selected data carrier transmits its identification data block to the station so that after such a selection operation the station knows the identity of the data carriers selected in the course of the executed selection operation. Subsequently, the station can address each selected data carrier individually in order to execute at least one communication operation with each selected data carrier, for example a read operation or a write operation or another operation.
It is a drawback of the known data carrier that, after selection of a given number of such known data carriers, in order to carry out a communication operation each of the selected data carriers must be addressed by way of a separate instruction so as to activate the relevant communication operation. The individual addressing of each selected data carrier by means of a respective instruction leads to a comparatively long communication interval; this is detrimental considering the need for as fast as possible communication with an as large as possible number of data carriers. Furthermore, because of the individual addressing of each selected data carrier by way of a respective instruction, a station arranged to communicate with the selected data carriers must generate and transmit a number of instructions which corresponds to the number of selected data carriers and hence produce a number of modulation steps, proportional to the number of instructions, in a carrier signal which serves for the transmission of the instructions to the data carriers and is in this case amplitude modulated; consequently, comparatively high levels occur in the range of the side bands of the amplitude modulated carrier signal used to transmit the instructions; in many countries this gives rise to conflicts with the rules and regulations concerning radio interference or radio interference limits.
It is an object of the invention to eliminate the described problems and to provide an improved data carrier of the kind set forth in the first paragraph as well as an improved circuit of the kind set forth in the second paragraph. In order to achieve this object, a data carrier of the kind set forth in the first paragraph according to the invention is characterized in that the circuit of the data carrier includes time slot fixation means by means of which fixation means, subsequent to the processing of the acknowledge data block by means of the third processing means, the respective nth time slot of successively running time slot sequences can be fixed for the circuit of the data carrier, and that the circuit of the data carrier includes control means by means of which control means, after fixation of the circuit of the data carrier to the respective nth time slot, communication between the data carrier and a station can be enabled only during the respective nth time slot fixed for the circuit of the data carrier.
In order to achieve the described object, a circuit of the kind set forth in the second paragraph according to the invention is characterized in that the circuit is provided with time slot fixation means by means of which fixation means, subsequent to the processing of the acknowledge block by means of the third processing means, respective the nth time slot of successively running time slot sequences can be fixed for the circuit, and that the circuit includes control means by means of which control means, after fixation of the circuit to the respective nth time slot, communication between the circuit and a station can be enabled only during the respective nth time slot fixed for the circuit.
Using only few means the steps according to the invention ensure in a simple manner that, after selection of a number of data carriers constructed according to the invention, the station intended for communication with the selected data carriers need generate and transmit only a single instruction in order to activate a desired communication operation with each of the selected data carriers; this instruction, being valid for all selected data carriers, ensures activation of the desired communication operation, subsequent to this instruction, during the time slot fixed for each of the selected data carriers. It is thus achieved that a single instruction for activating a communication operation suffices to carry out such a communication operation with each of the selected data carriers successively, resulting in a communication interval of optimum short length. Moreover, it is thus achieved that a modulated carrier signal which is transmitted by a station in order to transmit the instruction to the data carriers according to the invention includes only the modulation steps required for the transmission of this single instruction, so that only small level values occur in the range of the side bands of the modulated carrier signal and conflicts with rules and regulations concerning radio interference or radio interference limits are definitely avoided.
It has been found that it is very advantageous to take the steps disclosed in the Claims 2, 3 and 5, 6, respectively, for a data carrier and a circuit according to the invention, because these steps enable a very simple and reliable implementation.
These and other aspects of the invention will be apparent from the embodiment described hereinafter.